1. Field of the Invention
The present invention relates to a protective device or a safety cap that covers and protects the pressure release valve of a pressure cooker and to a pressure cooker installed with such a protective device.
2. Prior Art
A pressure cooker is a cooking utensil (pot) that utilizes high-temperature and high-pressure steam to cook food inside the pot. The pot and its lid are designed to create an airtight space inside the pot. When the pot is heated, the air inside expands. The expanding air inside the pot is unable to escape, so the atmospheric pressure within the pot increases. As the atmospheric pressure increases, the boiling point of water also increases. Thus, a pressure cooker enables the water or moisture inside the pot to become hotter than it would under the normal atmospheric pressure.
With a conventional cooking pot, the water inside a pot turns into steam at around 100° C. (212° F.). The steam freely escapes the pot, leaving the atmospheric pressure within the pot close to normal and the temperature close to 100°. Consequently, a large portion of the heating energy applied to the pot is wasted in warming the surrounding air.
In addition to creating a high-pressure environment within a pot, a pressure cooker also makes the water in a pot, in addition to the moisture within food, hotter than 100° C. and this impacts cooking in three ways. First, food cooks much faster in a high-pressure and high-temperature environment and requires far less cooking or heating time. The cooking time is shortened to one-third or one-fourth of the time required for a conventional cooking pot. Second, the decreased cooking time and trapped steam results in greater energy efficiency. A pressure cooker generally requires only one-fourth to one-third of the energy of a conventional cooking pot. Third, high-temperature and high-pressure cooking significantly improves cooking in high altitudes and in cold climates.
Unfortunately, there is an omnipresent risk, which is explosion caused by too much pressure inside the pot. This risk is very real because a pressure cooker prohibits the free circulation of air between the interior and the exterior of the pot and cooks food under high-pressure and high-temperature conditions. Today's pressure cooker manufacturers alleviate this risk in many ways, including: using sturdier materials to construct pots; utilizing a timer to control the length of heating time; installing a pressure gauge to monitor the atmospheric pressure inside; and installing a pressure release valve, which is the most widely used method.
A pressure release valve is a device that is physically attached to a pressure cooker. Its function is to release the pressurized air in a pot when the atmospheric pressure within the pot exceeds a pre-set point. The valve is usually installed in the pressure cooker lid. The interior portion of the valve is shaped like a pipe, and it has a closed end surrounded by four or five air intake apertures of 1 mm to 2 mm in diameter. The exterior portion of the valve is an air release nozzle. This nozzle is kept closed by the pressure of a weight device or a spring mechanism. When the pressure of the air or steam coming into the valve becomes greater than the pressure that keeps the nozzle closed, the valve opens and releases the inside air, which reduces the atmospheric pressure inside the pressure cooker.
While this type of safety device is very widely used, it is flawed in two major ways. First, the air intake apertures are easily clogged. When this occurs, the expanding air inside the pot has no means of release and the atmospheric pressure rises, which significantly increases the risk of explosion. The air intake apertures may be clogged by foods while cooking or by inadequate cleaning.
Second, putting aside the safety function that the valve actually provides, the valve's exterior appearance does not give the user an adequate sense of safety in using the pressure cooker. When a user sees only four or five very small clog-prone apertures (the number and size of the apertures vary according to size and type of the pressure cooker), he or she may feel more anxious than assured of the valve's safety. So as to increase this insecurity, the owner's manual accompanying the pressure cooker, in addition to other literature, repeatedly warn users about the importance of proper maintenance of the valve. While many consumers may realize the merits of a pressure cooker, unfortunately, they largely remain potential users.